⁷Li NMR Study on Irreversible Capacity of LiNi_0.8-xCo_0.15Al_0.05Mg_xO₂Electrode in a Lithium-Ion Battery

Abstract

Effects of magnesium and the charge/discharge process on the local structure of LiNi 0.8-x Co 0.15 Al 0.05 Mg x O 2 (x = 0, 0.05, 0.10) were examined by 7 Li MAS NMR. Two distinct 7 Li signals were observed at ca. 660 ppm and at ca. 570 ppm for the x = 0 material by the combined use of ultra-fast MAS (100 kHz) and high magnetic field (14 T). We attributed these two signals to two Ni-rich domains for the x = 0 material; the former Li signal is assigned to the Li site, whose local structure is expressed formally as LiNiO 2 and the latter to LiNi 0.83 (Co/Al) 0.17 O 2 . The intensities of these Ni-rich domains reduce significantly upon slight addition of magnesium. This leads us to conclude that magnesium preferably replaces nickel in the Ni-rich domains. After the first charge/discharge process, the signal intensities at 500∼750 ppm assigned to the Ni-rich domains in the x = 0 material decrease appreciably. From this, we conclude that the lithium ions responsible for the irreversible capacity after the first cycle belong to the Ni-rich domains, and the reduction of the amount of the Ni-rich domains due to magnesium substitution is responsible for the improved cyclic performance of the x > 0 material as a positive electrode material.

Identifying the Distribution of Al3+ in LiNi0.8Co0.15Al0.05O2

“…Comparison of the calculated spectra with experimental spectra (Figure 5b) indicates there is superb agreement between the experimental and the calculated dynamic JT spectrum. Our analysis of the 7 Li NMR spectrum differs slightly from that recently reported by Murakami et al 67 In their analysis of a NCA spectrum obtained at 14 T, they utilized the correlation of Delmas and co-workers 31 where they assigned three isotropic resonances, two dominant peaks associated with 6 and 5 Ni 3+ nearest neighbors and another broad peak associated with 1 to 4 Ni 3+ nearest neighbors. The deviation of intensity of the sites from a random solution model was attributed to Ni-rich and Ni-poor domains.…”

Solid-state NMR meets electron diffraction: determination of crystalline polymorphs of small organic microcrystalline samples

“…Such developments in micro-rotor-sized ultrafast MAS probes have now made 1 H-based methods routinely employed experiments in many research laboratories. Nowadays, ultrafast MAS rates of >100 kHz can be achieved with commercially available probes using rotors of diameter 0.7$0.8 mm (Parthasarathy et al, 2013;Kobayashi et al, 2013;Ye et al, 2014;Agarwal et al, 2014;Nishiyama, 2016;Nishiyama et al, 2014Nishiyama et al, , 2015Murakami et al, 2015;Penzel et al, 2015;Wickramasinghe et al, 2015;Andreas et al, 2016). In the present study, we demonstrate the possibility of using 1 H NMR to distinguish between crystalline polymorphs.…”

Fast magic-angle sample spinning solid-state NMR at 60–100 kHz for natural abundance samples

“…The first fast MAS (> 40 kHz) probe was developed by Samoson et al 5 , followed by the commercial products from the makers of the NMR spectrometers. The maximum attainable MAS frequency has now reached beyond 100 kHz on the commercially available probes 11,12,13,14,15,16 . Since the fast MAS probe accompanies micro-sized sample coil, the benefit of such probe is not only limited to the spinning frequency but also to micro coil NMR.…”

“…The peaks marked with * are the spinning side bands. Reproduced from Ref[16] with the permission of The Electrochemical Society.The other approach to get rid of the numerous SSBs is indirect detection method, more specifically by 1 H detection. Rotor-synchronized acquisition in the indirect dimension by virtue of which all the SSBs are folded to the centerband position holds the key to the success of the experiments especially for the samples associated with numerous SSBs.The ingenious idea to use HMQC to measure 14 N indirectly by 13 C has been independently developed by two different groups at the same time86,87 .…”